Finally tonight, a two-decade mystery left behind by a grandmother who loved puzzles, leaving her own secret code. How did they finally solve it? ABC's John donvan, now. Reporter: When Dorthy Holm, who hated the limelight but was close to her four grandkids departed 18 years ago from brain cancer she had lost the ability to speak. But she left behind this message inside a mystery strings of letters she scribbled in her last days that spelled nothing. Or did they? Her granddaughter, Janna, was 11 at the time. Part of me thought it was a code she was leaving. Reporter: But if it was a code, no one in the family could break it. But this week, a lightening bolt when Janna, on a lark, decided to take this mystery to a world of strangers. Posting the code online. They were on it immediately. Did she ever sings songs to you dad, one person asked. Another came up with, was she a religious woman? Religious, wait, those letters, aaa. Maybe, one person posted, that's amen, amen, amen. And then the breakthrough ofwaihhbth. Recognize that? Someone out there did. It's a prayer. Our father who art in heaven hallowed by thy name. Reporter: 18 years Dorthy Holm settling with god it seems. Those other letters mostly unsolved. Those code breakers are still at it. But they mean something. And for Janna knowing that means everything. John donvan, ABC news, Washington.

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